This document provides an introduction to machine elements and power transmission devices taught in the second semester of a mechanical engineering course. It discusses various machine elements like shafts, keys, couplings, bearings, clutches, and brakes. It also covers power transmission devices such as belt drives, chain drives, and gear drives. The document describes the function, types, materials, and design of these common mechanical components.

1. WELCOME
IN
SEM II
By prof. N. s. Surner

2. Machine elements,
Power Transmission Devices
UNIT NO.I
INTRODUCTION TO MECHANICAL
ENGINEERING

3. UNIT I
INTRODUCTION TO MECHANICAL ENGINEERING
 Mechanical Elements
Function, Sketch, Description & Uses of –
• Shaft
• Axle
• Keys ( Parallel Keys )
• Coupling ( Rigid Flanged Coupling )
• Bearing ( Ball Bearing )
• Clutch ( Single Plate Clutch )
• Brake ( Disc Brake )
 Power Transmission Devices
Construction, Working, Comparison & Applications of –
• Belt Drive ( Flat & V Belt )
• Chain Drive
• Spur gear drive arranged with simple gear train

4. Introduction
What is Machine?
Machine is a device consisting of various elements arranged
together, so as to perform the prescribe task to satisfy human
needs.
Eg: A pump-set is a machine in which the input is electrical energy,
the pump-set utilizes the electrical energy to perform the
prescribed task of lifting water to the desired location (output).
INPUT
(Source of energy)
MACHINE
(Arrangement of
elements)
OUTPUT
(Prescribed Task)

5. Machine Elements
• Machine element is an individual component or a group of
components of a machine which performs a specific function.
• Its function may be of holding the components together, to transmit
power or to give supports.
• Depending upon these functions only, the machine elements are
following types.
1) Machine elements used for holding the components.
2) Machine elements used for transmitting the power.
3) Machine elements used for support of other components.

6. Machine elements
Machine
elements
Holding
elements
Supporting
elements
Power
transmitting
elements

7. Machine Elements
• Machine elements used for holding the components :-
These type of machine elements include nuts and bolts,
screw, cotters, keys, couplings, pins, revettes.
• Machine elements used for transmitting the power :-
Machine elements like gears, shafts, clutches and brakes,
pulleys, belts, chain, sprocket, are used to transmit power from
one place to another.
• Machine elements used for support of other components:-
Machine elements like bearings, axles, brackets, hangers
etc. are used to give support to rotating or stationary members.

8. MECHANICAL SYSTEM
MACHINE
SHAFT
BEARING
KEYS
PRIME
MOVER
COUPLING
COUNTER
SHAFT
GEAR
SPINDLE
MACHINE TOOL
WORK PIECE BASE
PULLEY 1
PULLEY 2
BELT
CLUTCH
MAIN
SHAFT

9. Shaft
Introduction
A shaft is a rotating member/machine element, which is used to transmit
power from one place to another. In order to transfer the power from one shaft to
another the various members such as pulleys, gears, crank etc. are mounted on it.
These members are mounted on the shaft by means of keys or splines.

11. Types of shafts
1. Transmission 2. Machine shafts
Used to transmit the
power between the
source and the machine
1. Line shaft
2. Counter shaft
It is short rotating shaft
which forms an integral
part of the machine.
1. Spindle
2. crankshaft

12. Axles
• It is non-rotating machine element which is used to support
rotating machine elements like : wheels, pulleys etc.

13. Sr. No. Shaft Axle
1 Rotating member Non-Rotating member
2 Used to transmit the torque and support the
transmission elements, like: gears, pulleys
Only used to support the transmission
elements, like: wheels, pulleys etc
3 It is subject to torque, bending moment and axial force It is subjected to bending moment and
axial force
4 Example- line shaft, counter shaft, spindle, crankshaft Example:- front axle of car, wheel axle of
motorcycle etc.

14. Types of Shafts
Types :-
1) Axle
An axle is stationary shaft i.e. non
rotating member, which supports a
rotating element like wheel or
hoisting drum and fitted to the
housing by means of bearings. Axle
is subjected to bending load only
and does not transmit any useful
torque.
e.g.
• rear axle of railway wagon
• axle of motor car
• supporting wheels.
A ) Machine shaft:
These shafts form an integral part of the machine itself.
e.g. crank shaft of an I.C. engine.

15. Types :-
2) Spindle:
A spindle is a short rotating shaft.
Spindles are used in all machine
tools to give motion to a cutting
tool or to a work piece.
e.g.
• spindle of drilling machine.
• drive shaft of lathe.

16. Types of Shafts
Types :-
1) Main shaft
It is a primary shaft, which is
driven by the machine shaft and from
which the power is supplied to the
counter shaft.
2) Countershaft
It is a secondary shaft, which is
driven by the main shaft and from
which the power is supplied to the
machine components.
B) Transmission shaft:
These shafts transmit power from the source of power to the machine which absorbs
that power.
e.g. the power is transmitted from motor to compressor by means of a
transmission shaft.
The transmission shaft is usually circular in cross section. The shaft is always stepped
(having different cross sections of shafts) for positioning transmission elements like
gears, pulleys and bearings. Transmission shafts may be solid or hollow.

17. Types based on structure of Shafts
• Hollow shafts are lighter than
solid shafts. They have more
strength per kg weight of
material compared to solid
shaft.
• The various types of shafts are
as shown in Fig.
• The examples of the hollow
shafts are propeller shafts.
• Main shaft between air
compressor and gas turbine in
air craft engine.

18. Shaft Material
• The material used for the shaft should have the following properties
1) It should have high strength.
2) It should have good machinability.
3) It should have good heat treatment properties.
4) It should have high wear resistant properties.
5) It should have sufficient hardness.
6) It should be corrosion resistant in marine or corrosive
environments.
7) It should have high modulus of elasticity.
• The material commonly used for shaft is mild steel. The carbon steel is
also used where strength, wear resistance and facility of heat treatment
is needed.

19. Keys
A key is a machine element used on shafts to secure the rotating elements
like gears, pulleys or sprockets and prevent the relative motion between the
two. It is always inserted parallel to the axis of the shaft. Keys are used as
temporary fastenings and are subjected to considerable crushing and shearing
stresses.
A keyway is a slot or recess in a shaft and hub of the pulley to accommodate
a key.
Materials used:
 Plain carbon steels
 Alloy steels

20. • A key performs following two basic functions.
1) The primary function of key is to transmit the torque from the
shaft to the hub of machine element and vice-versa.
2) The second function of the key is to prevent relative rotational
motion between the shaft and mounted machine element like gear or
pulley.
• In most of the cases, key also prevents axial motion between the
elements.
• A keyed joint consisting of shaft, hub and key is illustrated in Fig.
• A recess or slot machined on the shaft and or in the hub to
accommodate the key is called as key way.
• One key way is usually cut by milling machine.
• Keys are designed in order to withstand shear and compressive stresses
resulting from transmission of torque.
• Generally, material of the key is selected, which has less strength than
the shaft material.

21. Types of Keys
• Keys are broadly classified as
a) Saddle keys
b) Sunk keys
c) Round key
d) Splines

22. Keys

24. Parallel key
Parallel keys are the most widely used. They have
a square or rectangular cross-section. Square keys
are used for smaller shafts and rectangular faced
keys are used for shaft diameters over 6.5 in
SS- 410 & SS- 316 material
used in automobile industries, Textile Industries, machine tool industries,
Motor & pump Industries, Cement Industries etc

26. Saddle Keys
•Saddle keys are fitted only in the key way of one
member of the mating surface i.e. either shaft or hub.
•Saddle keys are only of uniform width, and tapered in
thickness along the length.
•Power transmission of the saddle key is due to the
frictional forces set up between the keys and the shaft.
•Saddle keys are of two types -
i) Flat saddle key
ii) Hollow saddle key

27. Flat Saddle Key
•The flat saddle key is a
taper key which fits in a
key way in the hub and is
flat on the shaft as shown
in Fig.

28. Hollow Saddle Key
• A hollow saddle key is a taper
key which fits in a key way in
the hub and its lower surface
of the key is hollow or curved
to fit on the curved surface of
the shaft as shown in Fig.

29. •Advantages of Saddle Keys
1) Construction is simple.
2) Mounting cost is less as compared to other keys as there is
key way on the hub only.
3) No weakning of shaft as there is no key way.
•Disadvantages of Saddle Keys
1) Used for transmission of lighter loads only.
2) No positive transmission of power as means of power
transmission in friction.
•Applications
Used for light loads only like temporary fastening in fixing
and setting of eccentric cams etc.

30. Sunk Keys
• Sunk keys are inserted half in the key way of hub and half in the
key way of the shaft. Sunk keys are of uniform width and
tapered in thickness along the length.
• Power transmission of the sunk key is due to the tangential force
between key and mating surfaces. Due to the key inserted
between key ways in both hub and the shaft there is no relative
motion between the shaft and hub. Thus there is no slip between
them. Hence it is a positive drive.
• Sunk keys are of following types.
i) Parallel sunk key
ii) Taper sunk key
iii) Feather key
iv) Woodruff key

31. Parallel SunkKey
A parallel key is square or
rectangular in cross
section and of uniform
thickness and width over
its length.
Parallel sunk keys with
rectangular and square
cross section is shown in
Figs.

32. Gib Headed Key
•The gib head keys are
ordinary sunk keys
tapered on top with a
raised head on one side
so that its removal is
easy. This is shown in
figure.

33. Feather Key
Some feather key
arrangements are
shown in figure.
A feather key is used
when one component
slides over another.
The key may be
fastened either to the
hub or the shaft and the
keyway usually has a
sliding fit.

34. Woodruff Key
A woodruff key is a form of sunk key
where the key shape is that of a
truncated disc, as shown in figure.
It is usually used for shafts less than
about 60 mm diameter and the keyway
is cut in the shaft using a milling cutter.
It is widely used in machine tools
and automobiles due to the extra
advantage derived from the extra depth.

36. Couplings
Coupling is a device used to connect two shafts together at their
ends for the purpose of transmitting power
Motor
Coupling
Pump

37. Uses of coupling
• To provide connection of shafts of units made separately
• To allow misalignment of the shafts or to introduce mechanical
flexibility.
• To reduce the transmission of shock loads
• To introduce protection against overloads.
• To alter the vibration characteristics

38. Types of coupling
• Rigid
• Flexible
• Universal
Rigid coupling
Flexible coupling
Universal coupling

39. Rigid coupling
Flange
Driven Shaft
Driving
Shaft
Key Hub
•Rigid couplings are used when precise shaft alignment is required
•Simple in design and are more rugged
• Generally able to transmit more power than flexible couplings
•Shaft misalignments cannot be compensated
Flanged Coupling

40. Flexible Coupling
Bush
FlangeFlange
Driving
Shaft
Driven Shaft
Pin
•A flexible coupling permits with in certain limits, relative rotation and
variation in the alignment of shafts
•Pins (Bolts) covered by rubber washer or bush is used connect flanges
with nuts
•The rubber washers or bushes act as a shock absorbers and insulators.

41. Elastomeric coupling (Tyre Coupling)
Bolt
Flange
Elastomeric member
Flange
•An assembly of components designed to connect axially oriented
shafts in order to provide power transmission
•Able to accommodate shaft misalignment through elastomeric
materials

42. Advantages and Limitations
Advantages
• Torsionally stiff
• No lubrication or maintenance
• Good vibration damping and shock absorbing qualities
• Less expensive than metallic couplings
• More misalignment allowable than most metallic couplings
Limitations
• Sensitive to chemicals and high temperatures
• Usually not torsionally stiff enough for positive displacement
• Larger in outside diameter than metallic coupling
• Difficult to balance as an assembly

43. Bearings
• Types of bearings:
• Rolling contact or anti-friction bearing
• Journal or sleeve bearings(sliding contact bearing)
Mechanical Engineering Dept. 43
Bearings are used for carrying loads while allowing
relative motion(rotation) with minimum friction

44. Mechanical Engineering Dept. 44
Bearings
Rolling Contact Bearings – load is transferred through
rolling elements such as balls, straight and tapered cylinders
and spherical rollers.

45. Mechanical Engineering Dept. 45
Journal (sleeve) Bearings – load is transferred through
a thin film of lubricant (oil).

46. Mechanical Engineering Dept. 46
Design Considerations
• Bearing life and reliability
• Bearing speed (rpm)
• Space limitation
• Accuracy
• Bearing load – radial, thrust (axial) or both
Radial loadRadial load
Thrust load
Bearings are selected from catalogs, before referring to
catalogs you should know the followings:

47. 47
Rolling Contact Bearings
• Deep groove ball bearing
• Angular contact bearings (AC)
• Self alignment ball bearing
1. Ball bearings
3. Thrust bearings
• Cylindrical bearings(straight roller
bearing)
• Needle bearings
• Tapered bearings
• Spherical bearings
2. Roller bearings
In general, ball bearings
are capable of higher
speeds and roller
bearings can carry greater
loads

48. Types of Ball bearings
Mechanical Engineering Dept. 48

49. Mechanical Engineering Dept. 49
Ball Bearings
Deep groove (Conrad) bearing
• Primarily designed to support radial loads, the thrust
capacity is about 70% of radial load capacity
• Load capacity is limited by the number of balls

50. Mechanical Engineering Dept. 50
Ball Bearings
Angular contact bearings (AC)
The centerline of contact between the balls and the raceway is
at an angle to the plane perpendicular to the axis of rotation.
• Used for high radial and thrust load applications
Extra support
in the back
Direction
of thrust

51. Self alignment bearing
Mechanical Engineering Dept. 51

52. Mechanical Engineering Dept. 52
Roller Bearings
Roller bearings have higher load capacity than ball bearings, load is
transmitted through line contact instead of point contact.

53. Cylindrical bearing
Mechanical Engineering Dept. 53

54. Needle bearing
Mechanical Engineering Dept. 54

55. Mechanical Engineering Dept. 55
Roller Bearings
Bearing design uses barrel shaped rollers. Spherical roller bearings
combine very high radial load capacity with modest thrust load capacity
and excellent tolerance to misalignment.

56. Ball thrust bearing
Mechanical Engineering Dept. 56

57. Mechanical Engineering Dept. 57
Mounting Bearings
Pillow Block Flange
Common mounting, inner ring
held in position by nuts threaded
onto the shaft.
Alternative method, inner ring is
press fitted onto the shaft.
Two-bearing mounting

58. CLUTCHES
Objectives
• Describe the basic clutch parts
• Explain the operation of the clutch
• Compare differences in clutch design
• Describe the different methods of releasing the clutch

59. Introduction
•Clutch
• Found on vehicles with manually shifted transmissions
• Disengages engine from transmission
• Releases engine from transmission during gear shifts
• Driver controls clutch application from inside the vehicle with
a clutch pedal
• Engine does not make sufficient torque at lower rpm to be able to move the car
• Clutch must gradually couple rear wheels to engine

60. Clutch Parts and Operation
• Clutch parts
• Flywheel
• Pressure plate
• Friction disc
• Release mechanism
• Clutch disc pushed against flywheel with enough force
• Disc will rotate with flywheel

62. Clutch Disc
• Characteristics
• Clutch hub: inner part of disc and has splines
• Torsional dampers: absorb shock
• Clutch disc has facings made of friction material
• Contain molded or woven asbestos
• Facings riveted to both sides of cushion plate
• Cushion plate is riveted to disc plate
• Clutch is engaged: air is trapped in grooves
• Clutch is released: trapped air pushes disc away from pressure plate and flywheel

63. Pressure Plate
• Pressure plate is cast iron plate
• Part of cover assembly
• Cover assembly is bolted to the flywheel
• Clutch disc is wedged between pressure plate and flywheel
• Space between pressure plate and flywheel is less than thickness of
clutch disc
• Engine and transmission are physically connected when clutch pedal
released

64. Types of Clutch Covers
• Clutch covers types
• Coil spring
• Diaphragm
• Other designs are less
common

65. Coil Spring Clutch
•Pressure plate springs are preloaded when clutch
cover assembled at factory
• Springs are compressed further when cover assembly is
bolted to flywheel
• Clutch is engaged: pressure plate exerts 1000-3000 pounds
force on the disc
• Disc worn out: ten percent more torque carrying capacity
left in the clutch than engine can deliver

66. Release Levers
• Attached to cover assembly at pivot points
• Pushing clutch pedal moves pivot lever
• Pulls pressure plate away from flywheel
• Advantages of coil springs
• More coil springs can be installed
• Centrifugal force applies clutch more tightly
• Disadvantages of coil springs
• More pedal pressure required
• Clutch applied less heavily as disc wears
• Must be precisely balanced after assembly

67. Diaphragm Clutch
• Diaphragm spring replaces release levers and coil springs
• Diaphragm pivots off pivot rings when clutch pedal is depressed
• Advantages
• Requires less effort and takes up less space
• Spring pressure becomes greater as disc wears
• Well balanced
• Dual mass flywheel: reduces noise and vibration
• Allows smoother gear shifting

69. Pilot Bearing or Bushing
• Engine side of transmission input shaft
• Supported by sealed pilot bearing or sintered bronze bushing
• Some FWD transaxles do not use pilot bearing

70. Release Bearing
• Allows pressure plate release mechanism to operate as
crankshaft rotates
• Slides on the front transmission bearing retainer
• Lubricated and sealed at the factory
• Self-centering release bearings
• Used on FWD cars
• Do not use pilot bearing in the crankshaft
• Specially designed release bearings
• Found on vehicles that have pressure plates that pull to release

71. Clutch Fork
• Release bearing hub has provision to attach it to the clutch
fork
• Clutch fork fits between release bearing and clutch cable or linkage
• Has pivot shaft, pivot ball, or raised area in the bell housing off which it pivots

73. Clutch Release Methods
•Clutch pedal operates clutch fork using:
• Linkage
• Cable
• Hydraulic cylinders
•Clutch start switch
• Included on the clutch pedal
• Prevents engine from starting unless the clutch pedal is
depressed

74. Clutch Cable
•Some cars use a cable to operate the clutch
• Adjustment remains the same as the engine moves
• Develop friction and wear with repeated use
•Linkage can push on clutch arm
• Cable can only pull on it
•Pivot point of fork
• Must be on the outside of input shaft
• Away from cable end

76. Hydraulic Clutch Operation
•Characteristics
• Hydraulic clutches are found on many manual
transmission–equipped vehicles
• Master cylinder input piston: connected to clutch pedal
• Output piston: located in reaction or actuator cylinder (i.e.,
slave cylinder)
• Difference between clutch master cylinder and brake
cylinder
• Clutch master cylinder does not have a fill port or residual check valve

77. Clutch Free Travel
•Free travel
• Usually adjusted to about one inch at pedal
•Newer vehicles have self-adjusting clutches
• Maintain contact between release levers and release bearing
•Standard release bearings
• Don’t remain in constant contact with clutch cover
•Some vehicles have self-adjusting cables
• Spring-loaded sector gear pinned to pedal arm
• Clutch released: pawl lifted and raised

80. Dual Clutch Transmissions
• Being used by several manufacturers
• Two clutches connect to two separate geartrains within one transmission
housing

81. 81
Purpose of the Clutch
•Allows engine to be disengaged from transmission
for shifting gears and coming to a stop
•Allows smooth engagement of engine to
transmission

82. 82
Clutches
Rear wheel drive
Front engine
Rear engine
Mid engine
Front wheel drive

83. 83
Clutches
•Coil spring
pressure plate
•(cover and
pressure plate)

84. 84
Clutches
• 44-3 Construction of the
Clutch
Splines to input shaft
Of transmission
Clutch Disk or
Friction Disk
READ ON

85. 85
Pilot Bushing or bearing
READ ON

86. 86
Clutches Flywheel bolts
to crankshaft
Pressure plate & cover
bolt to flywheel
If there is a chance you will be reusing
pressure plate, make alignment marks
to flywheel to maintain proper balance
BEFORE removal
When unbolting pressure plate from the
flywheel, remove bolts evenly as not to
bend the cover. REMEMBER, this is
under high spring pressure.

87. 87
Flywheels
•Add weight to crank for non-power strokes
•Has ring-gear for cranking engine (usually replaceable)

88. 88
Clutches
Bolted to Crank
(friction disk) splined to transmission
Input shaft
(throw-out bearing
T/O bAearing) allows
to push on rotating
clutch fingers
Bolted to flywheel - Applies
the spring force to clamp the
friction disk to the flywheel
(clutch fork) pushes
T/O bearing to release
rotating clutch
Pilot bushing or bearing in center
of flywheel or crankshaft, supports
the end of input shaft

89. 89
Pressure Plate
PivotsT/O bearing
Moves pressure
Plate right
Releases friction disk
from flywheel

90. 90
Clutch terms
•Clutch disengaged
• Clutch pedal is in or down
•Clutch engaged
• Clutch pedal is out or up
What would it mean if someone said the clutch pedal
Is engaged?
Make sure you know if you are talking about
the clutch or the clutch pedal !!!

91. 91
Clutches

92. 92
Throw out bearings
•Most need clearance between fingers of pressure
plate so it isn’t spinning all the time (free play)
•Riding the clutch (foot resting on pedal)
• Pushes T/O bearing into pressure plate fingers
• Causes it spin constantly
• Wearing it out too soon
• Releases some of clutch spring pressure
• Causing clutch to slip

93. 93
Free play
• Clearance between T/O bearing and clutch fingers
• Measured at clutch pedal
• Usually 1 ½ inches of free movement
• Goes away as clutch disk wears thinner
• Some manufactures use T/O bearings that always ride on the
clutch fingers
• Usually self adjusting